Investment and Disposition Activities - 2014 Transactions - Additional Information (Detail)																							1 Months Ended		3 Months Ended	7 Months Ended	12 Months Ended
	Mar. 05, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 23, 2014 USD ($)	Dec. 09, 2014 USD ($)	Dec. 02, 2014 USD ($)	Nov. 25, 2014 USD ($)	Oct. 30, 2014 USD ($)	Oct. 24, 2014 USD ($) Property	Oct. 22, 2014 USD ($)	Oct. 20, 2014 USD ($)	Oct. 16, 2014 USD ($)	Oct. 15, 2014 USD ($)	Oct. 01, 2014 USD ($)	Aug. 07, 2014 USD ($)	Aug. 06, 2014 USD ($) Office	Aug. 01, 2014 USD ($)	Jul. 07, 2014 USD ($)	Jun. 25, 2014 USD ($)	May. 01, 2014 USD ($)	Mar. 05, 2014 USD ($)	Feb. 26, 2014 USD ($)	Jan. 10, 2014 USD ($)	Jun. 30, 2014 USD ($)	Feb. 07, 2014 USD ($)	Mar. 31, 2014 USD ($)	Jul. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) Investment	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Investment And Disposition Activities [Line Items]
Outstanding loans acquired for aggregate price																										$ 31,492,000			$ 21,437,000
Payment of interest accrued																										15,280,000			23,735,000
Principal payments received on loan receivable				$ 27,394,000
Distributions received from equity investments				6,565,000
Net proceeds				$ 33,959,000
Liquidation value of investment																$ 29,369,000
Sales of interest																								$ 42,900,000
Sale price net amount																								29,150,000
Gain (loss) on sale of loan																								$ 0
Proceeds from sale of interest in real estate property																										$ 56,423,000			38,690,000
Payment of loan																													$ 23,770,000
Playa Vista Mezzanine Loan [Member]
Investment And Disposition Activities [Line Items]
Mortgage loan on real estate, increase in principal balance																						$ 4,000,000
Mortgage loan on real estate, increase in interest rate																						1.50%
Mortgage loan on real estate, revised interest rate																						16.25%
Mortgage loan on real estate, share in increased loan amount																						$ 2,000,000
Share funded amount																						$ 1,992,000
Outstanding loans acquired for aggregate price																	$ 14,000,000
Ownership percentage																	50.00%
Payment of interest accrued																	$ 108,000
Premium amount included in purchase price																	$ 762,000
Legacy Orchard Loan [Member]
Investment And Disposition Activities [Line Items]
Retained interest																								2.50%
Hotel Wales Loan [Member]
Investment And Disposition Activities [Line Items]
Retained interest																								0.50%
Marc Realty [Member]
Investment And Disposition Activities [Line Items]
Gross proceeds from sale																5,770,000				$ 6,000,000
Gross proceeds from sale, cash received																				1,500,000
Gain on sale of equity investments																				69,000							$ 69,000
Gross proceeds from sale, note receivable																				4,500,000
Gain on sale of interest																				3,000							$ 3,000
Number of equity investments | Investment																											3
Liquidation value of investment																5,770,000
Edens Center and Norridge Commons [Member]
Investment And Disposition Activities [Line Items]
Loan secured by limited partnership interests, face amount																				$ 15,500,000
Loan secured by limited partnership interests, basis spread on variable rate																				12.00%
Loan secured by limited partnership interests, increase in basis spread on variable rate in each extended term																				1.00%
Loan secured by limited partnership interests, stated current interest rate																				10.00%
Loan secured by limited partnership interests, annual increase in stated current interest rate																				0.50%
Loan secured by limited partnership interests, term																											3 years
Description of Trust's participation interest in loan																											Upon satisfaction of the loan, the Trust will be entitled to a participation interest equal to the greater of (i) a 14.5% internal rate of return ("IRR") (increasing to 15.5% IRR after the initial term) and (ii) 30% (increasing to 40% after the initial term and 50% after the first extended term) of the value of the properties in excess of $115,000,000.
Loan participation interest IRR percentage																				14.50%
Loan participation interest IRR percentage after initial term																				15.50%
Loan participation interest percentage																				30.00%
Loan participation interest percentage after initial term																				40.00%
Loan participation interest percentage after extended term																				50.00%
Minimum value of properties for entitlement to loan participation interest																				$ 115,000,000
Fenway-Wateridge [Member]
Investment And Disposition Activities [Line Items]
Liquidation value of investment															$ 2,383,000
Norridge [Member]
Investment And Disposition Activities [Line Items]
Acquisition of issued and outstanding equities																				$ 250,000
Percentage of ownership interest																				0.375%
Edens Properties [Member]
Investment And Disposition Activities [Line Items]
Acquisition of issued and outstanding equities	$ 250,000
701 Seventh Avenue [Member]
Investment And Disposition Activities [Line Items]
Additional capital contributions																												$ 53,187,000
Capital contributions																												$ 106,624,000
Newbury Apartments Property [Member]
Investment And Disposition Activities [Line Items]
Net proceeds																					$ 5,106,000
Proceeds from sale of interest in real estate property																					27,500,000
Gain or loss on sale of property																					$ 4,422,000
Queensridge [Member]
Investment And Disposition Activities [Line Items]
Aggregate principal payments																									$ 2,908,000
Trust received, exit fee																									$ 1,787,000
Crossroads [Member]
Investment And Disposition Activities [Line Items]
Net proceeds																			$ 29,633,000
Gain or loss on sale of property																			5,723,000
Gross proceeds from sale																			$ 31,100,000
Stamford [Member] | Office [Member]
Investment And Disposition Activities [Line Items]
Net proceeds from distributions of venture															$ 9,450,000
Number of office properties | Office															7
The Shops at Wailea [Member]
Investment And Disposition Activities [Line Items]
Liquidation value of investment														$ 7,516,000
Net proceeds from loan repayment														$ 7,556,000
Amherst [Member]
Investment And Disposition Activities [Line Items]
Net proceeds																		$ 21,226,000
Proceeds from sale of interest in real estate property																		24,500,000
Gain or loss on sale of property																		946,000					$ 946,000
Revenue from reserve holdback																		2,449,000
Net proceeds from sale of real estate property																		$ 23,675,000					$ 24,500,000
Waterford [Member]
Investment And Disposition Activities [Line Items]
Gross proceeds from sale											$ 15,290,000
Net proceeds from sale of real estate property											$ 28,160,000
Liquidation value of property																28,160,000
5400 Westheimer [Member]
Investment And Disposition Activities [Line Items]
Liquidation value of investment																10,777,000
Net proceeds from loan repayment													$ 1,033,000
Proceeds from sale of interest in joint venture												$ 9,690,000
Kroger Atlanta [Member]
Investment And Disposition Activities [Line Items]
Gross proceeds from sale										$ 1,464,000
Net proceeds from sale of real estate property										$ 1,500,000
Liquidation value of property																2,000,000
Kroger Greensboro [Member]
Investment And Disposition Activities [Line Items]
Gross proceeds from sale							$ 1,709,000
Liquidation value of investment																2,500,000
Net proceeds from sale of real estate property							$ 1,750,000
Pinnacle II [Member]
Investment And Disposition Activities [Line Items]
Gross proceeds from sale									$ 4,967,000
Liquidation value of investment																4,989,000
Net proceeds from sale of real estate property									$ 5,017,000
San Pedro [Member]
Investment And Disposition Activities [Line Items]
Gross proceeds from sale								$ 23,090,000
Net proceeds from sale of real estate property								$ 23,800,000
Liquidation value of property																23,800,000
Ownership percentage in real estate investment								83.70%
Number of properties | Property								4
San Pedro [Member] | Apartment Building [Member]
Investment And Disposition Activities [Line Items]
Payment of loan								$ 150,000,000
Kroger Louisville [Member]
Investment And Disposition Activities [Line Items]
Gross proceeds from sale						$ 2,334,000
Net proceeds from sale of real estate property						$ 2,500,000
Liquidation value of property																2,500,000
1515 Market Street Loan Modification [Member]
Investment And Disposition Activities [Line Items]
Gross proceeds from sale					$ 40,304,000
Net proceeds from sale of real estate property					$ 82,345,000
Liquidation value of property																81,314,000
Burlington [Member]
Investment And Disposition Activities [Line Items]
Gross proceeds from sale		$ 2,475,000
Net proceeds from sale of real estate property		$ 2,850,000
Liquidation value of property																3,225,000
Sealy Northwest Atlanta [Member]
Investment And Disposition Activities [Line Items]
Gross proceeds from sale			$ 5,641,000
Liquidation value of property																$ 5,692,000